1. Field of the Invention
This invention relates to zoom lens systems and more particularly to an improved zoom lens system having macrophotography capabilities.
2. Description of the Prior Art
In the field of zoom lens systems, several techniques have heretofore been proposed for focusing in the macrophotography range. As the prior art is aware, the inclusion of a macrophotography range, is understood to refer to photographing objects at less than one meter, and in most cases with a magnification of the image. Many of the zoom lens systems that have incorporated macrophotography have required that either the entire zoom lens system or some varifocal lens group thereof be provided with a specific movement which is at variance with the movement required for normal zooming photography within the normal range of object distance. As a result, the arrangement of the lens elements, in a macrophotographic mode of operation is thus different from the normal lens arrangement and the resulting balancing of the various aberrations that are created intrinsically in a zoom lens system is disturbed. These aberrations are transferred to the image plane by the relay lens group and because the transferring magnification of the relay lens group is particularly high in the case of a telephoto zoom lens system, the resulting image characteristics are deteriorated to such an extent that no practical utility is possible unless the aperture is severely stop down. Obviously, this limits the speed and conditions under which macrophotography is possible.
Optical designers have realized that in order to design such a lens system wherein satisfactory optical performance is possible in a macrophotographic mode that it is necessary to sacrifice some of the optical performance attainable in the zooming photography mode of operation within the normal range of object distance. To avoid this result, it has been necessary in the prior art zoom lens systems capable of macrophotography to increase the number of lens elements in the lens system if it is desired to obtain satisfactory performances in both the normal zooming photography and macrophotography ranges.
An example of a varifocal lens system with macrophotography capabilities can be found in U.S. Pat. No. 3,994,572. An additional example wherein a focusing lens is shifted to its extreme foremost end and the front group of a relay lens is shifted toward the image plane, can be found in U.S. Pat. No. 3,659,921.
Other examples of prior art combinations of a zooming operation with macrophotography can be found in U.S. Pat. No. 3,912,373, U.S. Pat. No. 3,655,271, U.S. Pat. No. 3,613,544, U.S. Pat. No. 3,784,284 and U.S. Pat. No. 3,784,285.
A Japanese patent application which has been laid open to the public and identified as No. 51-6564, discloses a zoom lens operation wherein a variator and compensator lens group is shiftable for a zooming operation and at least a part of the relay lens group is shiftable for correcting undesirable variations in aberrations created during the zooming mode of operation. To date, there has been an inadequate effort to provide a correction of aberrations that occur in a macrophotography mode of operation while limiting the number of lens elements and providing an adequate aperture number to meet the needs of a versatile zoom and macrophotographic lens system.